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SOME EXAMPLES OF QUANTITATIVE E.B.I.C.
MODE FOR THE STUDY OF THE ELECTRICAL PROPERTIES OF DISLOCATIONS IN
SEMICONDUCTOR DEVICES
J. Bresse
To cite this version:
J. Bresse. SOME EXAMPLES OF QUANTITATIVE E.B.I.C. MODE FOR THE STUDY OF THE ELECTRICAL PROPERTIES OF DISLOCATIONS IN SEMICONDUCTOR DEVICES. Journal de Physique Colloques, 1983, 44 (C4), pp.C4-465-C4-468. �10.1051/jphyscol:1983455�. �jpa-00223075�
SOME EXAMPLES OF QUANTITATIVE E ~ B I I ,C, MODE FOR THE STUDY OF THE ELECTRICAL PROPERTIES OF DISLOCATIONS I N SEMICONDUCTOR DEVICES
J . F . ~ r e s s e '
Laboratoire de Microscopic Electronique, U. S. T . L., 34060 Montpellier Cedex, France
Resume - Une mesure simultanee des longueurs de d i f f u s i o n e t de l a duree de v i e - d e s p o r t e u r s m i n o r i t a i r e s permet d 4 @ t u d i e r 1 ' i n f l u e n c e de l a presence d ' u n reseau de d i s l o c a t i o n ou de j o i n t s de g r a i n s s u r ces deux parametres im- p o r t a n t s d ' u n d i s p o s i t i f .
A b s t r a c t - A simultaneous measurement o f t h e d i f f u s i o n l e n g t h and t h e l i f e - t i m e o f m i n o r i t y c a r r i e r s a l l o w s t h e s t u d y o f t h e i n f l u e n c e o f t h e presence o f a d i s l o c a t i o n network o r g r a i n boundaries on these two i m p o r t a n t
parameters o f semi conductor d e v i c e s .
Fundamentals o f E.B.1 .C. mode. P r i n c i p l e of d e t e c t i o n of e l e c t r i c a l l y a c t i v e d e f e c t s T h e o r e t i c a l model i z a t i o n s o f p e n e t r a t i o n of e l e c t r o n s , g e n e r a t i on o f m i n o r i t y c a r r i e r s and the c o l l e c t i o n o f t h e c a r r i e r s g i v i n g r i s e t o t h e E l e c t r o n Beam Induced C u r r e n t (E.B.I.C.) by a j u n c t i o n p e r p e n d i c u l d r o r p a r a l l e l t o the s u r f a c e have been w e l l supported i n t h e p a s t t e n y e a r s ( 1 ) ( 2 ) ( 3 ) and more r e c e n t l y f o r t h e t r a n s i e n t a n a l y s i s ( 4 ) ( 5 ) .
The 1 im i t a t i o n s and accuracy on t h e d e t e r m i n a t i o n o f t h e two i m p o r t a n t parameters d i f f u s i o n l e n g t h and l i f e t i m e o f m i n o r i t y c a r r i e r s a r e a c t u a l l y c l e a r l y d e f i n e d ( 6 ) . The presence o f e l e c t r i c a l l y a c t i v e d e f e c t s ( p o i n t - 1 i k e o r 1 ine-shape d e f e c t s ) can be i n t e r p r e t e d as a p e r t u r b a t i o n g i v i n g r i s e t o a c o n t r a s t i n E.B.I.C. mode ( 7 ) w h i c h has a s t r e n g t h g i v e n by
1 1 2
y = l3 (7-7) w i t h LD = D T ~ L~
where 1 i s t h e l e n g t h o f t h e d e f e c t LD and TD a r e r e s p e c t i v e l y t h e d i f f u s i o n l e n g t h and the l i f e t i m e a s s o c i a t e d t o the d e f e c t , L t h e d i f f u s i o n l e n g t h o f t h e m a t e r i a l . A p p l y i n g f o r T~ t h e known r e l a t i o n :
- 1
T D = (NDoDvth)
where N, i s the d e n s i t y o f r e c o m b i n a t i o n c e n t r e s i n s i d e t h e d e f e c t , t h e i r c a p t u r e c r o s s - s e c t i o n , vth the thermal v e l o c i t y o f m i n o r i t y c a r r i e r s , E.B.I.C. has been shown t o be a v e r y s e n i i t i v e technique f o r t h e d e t e c t i o n o f c l u s t e r s , d i s l o c a t i o n w i t h i m p u r i t y atmosphere o r e l e c t r i c a l l y a c t i v e c l e a n d i s l o c a t i o n ( 8 ) ( 9 ) o r t o s t u d y .the q u a l i t y o f t h e g r a i n s i n p o l y c r i s t a l l i n e m a t e r i a l s ( 1 0 ) .
' p r e s e n t a d d r e s s : C . N . E . T . PMS/SPD,196 rue de Paris,92220 Bagneux, France
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983455
C4-466 JOURNAL DE PHYSIQUE
L i f e t i m e o f m i n o r i t y c a r r i e r s measurercent b y E.B.I.C. mode m o n i t o r e d by a m i c r o - p r o c e s s o r .
F o r t h e range o f l i f e t i m e v a r y i n g f r o m 100 n s e c t o s e v e r a l psec. a system where a m i c r o p r o c e s s o r p i l o t s t h e o b t a i n i n g o f t h e t r a n s i e n t decay o f t h e E.B.1 .C. f o r a beam f i x e d a t a c e r t a i n d i s t a n c e f r o m t h e j u n c t i o n and g i v e s t h e data p r o c e s s i n g has been e s p e c i a l 1 y designed f o r t h i s purpose.
I I
E l e c t r o n Gun anodePower Amp1 if i e r E l e c t r o s t a t i c p l a t e r
C
4 I
I 1 I f
I
F i g . 1 - System u s i n g a m i c r o p r o c e s s o r f o r t h e l i f e t i m e measurement.
I
I
llpn
F i g u r e 1 shows t h e p r i n c i p l e o f t h e system. The c l o c k o f t h e m i c r o p r o c e s s o r generates t h e p u l s e s f o r t h e beam b l a n k i n g where t h e o f f p e r i o d can b e v a r i e d f r o m 10 psec t o 1 msec. The r i s e t i m e o f t h e v o l t a g e p u l s e s a p p l i e d t o t h e e l e c t r o s t a t i c p l a t e s i s l i m i t e d t o t h e r i s e t i m e o f t h e c l o c k o f t h e m i c r o p r o c e s s o r and t h e r i s e t i m e of t h e power amp1 i f i e r w h i c h t r a n s m i t s t h e v o l t a g e t o t h e p l a t e s .
c l o c k
*
I n o u r system t h e r i s e t i m e i s a b o u t 50 nsec,lower t h a n t h e range o f l i f e t i m e measured.
The a m p l i f i c a t i o n o f t h e s i g n a l ( u s u a l l y 1 amp i n t h e s t e a d y - s t a t e case) i s made b y a wideband a m p l i f i e r t o r e a c h t h e T.T.L l e v e l ( 5 v o l t s ) i n c l u d i n g t h e l e v e l o f t h e n o i s e ( a b o u t 1 v o l t i n o u r system). A sampler h o l d e r g i v e s t h e decay c u r v e as f u n c t i o n o f t i m e p o i n t by p o i n t w i t h sampling i n v e r v a l s o f 25 nsec o r 50 nsec.
-
M i c r o p r o c e s s o rData a c q u i s i t i o n and a v e r a g i n g ( u p t o 16 t i m e s ) i s made by a m i c r o p r o c e s s o r which can p l o t t h e decay c u r v e on a screen o r on a X - Y p l o t t e r o r p r i n t t h e numerical d a t a The s l o p e o f the t r a n s i e n t c u r v e i n l o g a r i t h m i c s c a l e can g i v e t h e v a l u e o f t h e l i f e t i m e a f t e r a c o r r e c t i o n t a k i n g i n t o a c c o u n t o f t h e d i s t a n c e s p o t - j u n c t i o n and t h e v a l qe o f t h e r e c o m b i n a t i o n s u r f a c e ( 4 )
.
E f f e c t o f d i s l o c a t i o n s on l i f e t i m e and d i f f u s i o n l e n g t h o f m i n o r i t y c a r r i e r s . D r a s t i c decrease i n d i f f u s i o n l e n g t h o f m i n o r i t y c a r r i e s have been observed i n GaAs
4 2
f o r a d i s l o c a t i o n d e n s i t y g r e a t e r t h a n 10 /cm ( 1 1 ) o t h e r l i f e t i m e measurements have been made u s i n g cathbdoluminescence i n 111-V compounds near a d i s l o c a t i o n which a l s o shows an i m p o r t a n t decrease o f t h e r a d i a t i v e l i f e t i m e near t h e d i s l o c a t i o n s ( 1 2 ) ( 1 3 ) .
s t u d y t h e semiconductor i s adapted t o t h e range o f l i f e t i m e which can be a c h i e v e d w i t h o u r system.
F o r example i n p o l y c r y s t a l l i n e S i l i c o n s o l a r c e l l s w i t h a l a r g e g r a i n s i z e t h e h o l e d i f f u s i o n l e n g t h can r e a c h 25 pm i n S i l i c o n N-type w i t h a r e s i s t i v i t y o f 10 nm.
The l i f e t i m e measured b y o u r system g i v e s a v a l u e i n t h e range o f a c c u r a c y o f t h e v a l u e which can be deduced u s i n g t h e E i n s t e ' n r e l a t i o n ( a b o u t 0.5 psec f o r a h o l e d i f f u s i o n l e n g t h o f 25 pm w i t h Dp = 12.5 cm / s e c ) . B u t f o r a n o t h e r t y p e o f S i l i c o n
h
p o l y c r y s t a l l i n e s o l a r c e l l (I?-type) t h e l i f e t i m e ~neasurement made by o u r system g i v e s a v a l u e o f t h e e l e c t r o n l i f e t i m e ~ n = 0.37 psec. The v a l u e o f Ln measured w i t h t h e E.B.I.C. c o n t i n u o u s g i v e s d i f f e r e n t v a l u e s v a r y i n g w i t h t h e l a t e r a l p o s i t i o n o f t h e beam on t h e c l e a v e d s e c t i o n . The v a l u e o f Ln can v a r y b y a f a c t o r two and has a maximum v a l u e o f about 10 pm.
The v a l u e o f Ln deduced f r o m t h e ~ f e t i m e
4.
measurement i s a b o u t 35 11m by a p p l y i n g t h e E i n s t e i n r e l a t i o n w i t h Dn = 36 cm /sec.The d i s c r e p a n c y between t h e two v a l u e s o f Ln can o n l y be e x p l a i n e d by t h e presence of t h e columnar s t r u c t u r e o f t h e g r a i n s w h i c h can l i m i t t h e c o l l e c t i o n o f c a r r i e r s i n t h e case o f t h e c o n t i n u o u s E.B.I.C. measurement as shown i n F i g . 2.
P] E l e c t r o n beam C o l l e c t
Scanned 1 in e
F i g . 2 - Columnar s t r u c t u r e o f a S i l i c o n s o l a r c e l i and p o s i t i o n o f t h e beam f o r t h e E.B. I .C. measurements ( c o n t i n u o u s and t r a n s i e n t ) .
N e v e r t h e l e s s when t h e beam i s f i x e d , i n t h e t r a n s i e n t case, t h e c o l l e c t i o n o f c a r r i e r s can be made by a p a t h i n t h e columnar s t r u c t u r e and t h e s t r u c t u r e has p r a c t i c a l l y no e f f e c t on t h e E.B.I.C. decay.
As p r e v i o u s l y shown i n o t h e r m a t e r i a l s , l i k e GaAs, t h e d i f f u s i o n l e n g t h o f t h e m i n o r i t y c a r r i e r s can be l i m i t e d t o t h e v a l u e o f t h e average s p a c i n g o f t h e d i s l o c a t i o n s ( 1 1 ) .
The same o b s e r v a t i o n has been made f o r t h e h o l e d i f f u s i o n l e n g t h i n CdS f o r a s t i u c t u r e CuxS/CdS where t h e g r a i n s i z e i n CdS i s a b o u t 0.5 um w h i c h l i m i t s t h e v a l u e o f t h e h o l e d i f f u s i o n l e n g t h t o a b o u t t h e same v a l u e ( 1 4 ) .
Conclusion
--
The simultaneous measurement o f d i f f u s i o n l e n g t h and l i f e t i m e o f m i n o r i t y c a r r i e r s by E.B.I.C. mode can be a v e r y i m p o r t a n t t o o l f o r t h e s t u d y o f t h e e f f e c t o f t h e d i s l o c a t i o n i n semiconductors.
C4-468 JOURNAL DE PHYSIQUE
I n t h e case o f S i l i c o n where t h e d i f f u s i o n l e n g t h i s l i m i t e d t o t h e average spacin2 o r t h e g r a i n s i z e . The l i f e t i m e measurement made by E.B.I.C. t r a n s i e n t p e r m i t t o r e a c h t h e r e a l v a l u e o f t h e d i f f u s i o n l e n g t h o f t h e m a t e r i a l .
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( 1 2 ) RASUL A., DAVIDSON S . K , IITRI/SEM, Om JOHARI Ed. 1 (1977) 233 ( 1 3 ) BOULOU M., SCHILLER C., J . M i c r o s . S p e c t r o s c . ElecFron. 6, (1981) 3 9 - ( 1 4 ) BRESSE J.F., EUREM (1980) 1, (1980) 358
Conf :
ACKNOULEDGHENTS : He w i s h t o thank D r R. ALABEDRA and D r J.C. MANIFICIER (U.S.T.L.
-- MONTPELLIER) f o r t h e d e v i c e f u r n i t u r e and h e l p f u l d i s c u s s i o n s .
